Abstract: In order to explore easy, frequent, convenient and accurate method for measuring heparin sodium potency, based on the reaction of heparin sodium with Azure A, the best buffer for the reaction was firstly screened, single-wavelength method, dual-wavelength method and the first order derivative method were further compared. According to the suitability and feasibility, the best method was finally determined. The results showed that Tris-HCl buffer could replace barbiturates buffer totally, when measured low potency, three methods for measurement accuracy heparin sodium potency were feasible and the accuracy order from low to high was that : single-wavelength method, dual-wavelength and the first order derivative method. When measured low potency, only the first order derivative worked. The first order derivative method of optimum conditions were Tris-HCl buffer concentration 0.05mol/L, pH=8.6, Azure A concentration 0.2mg/mL. The squared correlation coefficient was 0.9980, the variation coefficients of this method was 0.43%.